Only we already do that. People aren't punished for being an addict, they are punished when caught with large quantities of drugs or driving while under the influence of drugs. There is no crime for being high.
All legalizing drugs would do is create even more addicts by virtue of more people using them due to no longer fearing legal repercussions for doing so. Not to mention many other potential unintended consequences. Many of the drugs you people advocate legalizing are incredibly addictive. Legalizing them (as well as legally manufacturing them, regulating them, and taxing them that comes with that) would make them FAR more expensive... People will still be as addicted to them. IE: Addicts will be even more likely to ruin their lives financially... Not to mention other potential increases in crime to finance their addictions, etc...